1. Field of the Invention
The present invention relates to a lens barrel, and in particular the invention relates to a lens barrel that moves a lens group by turning operations of a zoom ring in the optical axis direction and stops the same at a plurality of zoom positions, and at the same time, is capable of focusing adjustment from infinity to near distance. A lens barrel according to the invention is applicable to a camera for a 35 mm wide film and a digital camera, etc.
2. Description of the Related Art
A magnification varying unit that has been proposed in Japanese Patent No. Hei 6-100707 and a zoom position changing unit that has been proposed in Japanese Laid-Open No. Hei 9-80291 are capable of varying the power and focusing adjustment by turning operations of a single zoom ring.
FIG. 13 and FIG. 14 are general views of the major parts of a magnification varying unit that have been proposed in Japanese Patent No. Hei 6-100707, that is, views showing the relationship of a turning angle of the zoom ring and an amount of movement of a lens group in the optical axis direction. The power varying unit is composed of two lens groups and is capable of changing zoom positions and carrying out focusing adjustment by turning operations of the zoom ring.
101 denotes a positive lens unit, 102 denotes an aperture that is concurrently used as shutter blades, 103 denotes a negative lens unit, and 104 denotes an image pick-up plane. Herein, arrow C indicates an amount of movement of the positive lens unit 101 in the optical axis direction with respect to the turning angle of the zoom ring. Also, arrows M1 through M4 and arrows N1 through N3, respectively, indicate an amount of movement of the negative lens unit 103 in the optical axis direction with respect to the turning angle of the zoom ring.
When the zoom ring is located at a position where the turning angle is 0xc2x0, the positive lens unit 101, shutter blades 102 and negative lens unit 103 are located in such a relationship shown at the upper side in FIG. 1 through FIG. 13. That is, the power varying unit is at a short focal length (hereinafter called xe2x80x9cWIDExe2x80x9d) and the lens focusing is set to infinity (hereinafter called xe2x80x9c∞xe2x80x9d).
Also, when the zoom ring is located at a position where the turning angle is 180xc2x0, the positive lens unit 101, shutter blades 102 and negative lens unit 103 are located in such a relationship as depicted at the underside in FIG. 13 with respect to the image pick-up plane 104. That is, the power varying unit is at a long-focal length (hereinafter called xe2x80x9cTELExe2x80x9d), and at the same time, the lens focusing is set to ∞).
If the zoom ring is turned by 30xc2x0 around the optical axis from a state where the lens focusing is set to ∞ at a zoom position of WIDE, the positive lens unit 101 is moved in the optical axis direction in compliance with the arrow C, and the negative lens unit 103 is moved in the optical axis direction based on the arrow M1. That is, where the turning angle of the zoom ring is in a range from 0xc2x0 through 30xc2x0, the positive lens unit 101 and negative lens unit 103 are taken out in the optical axis direction with a fixed-spacing condition secured, whereby only a focusing adjustment to the near distance of the lens groups is carried out with the WIDE condition maintained. Herein, the lens is focused to the near distance when the zoom ring is positioned at a turning angle of 30xc2x0.
If the zoom ring is further turned around the optical axis, the positive lens unit 101 is moved in the optical axis direction in compliance with the arrow C, and at the same time, the negative lens unit 103 is moved in the optical axis direction based on the arrow N1, wherein, when the turning angle of the zoom ring is set to 60xc2x0, the lens group power is changed to a higher power by one rank.
If unit operator changes the mode to normal (NOM) mode in order to slightly further increase the magnification of the lens group, the zoom ring further turns to a position of 120xc2x0. Herein, when the zoom ring turning angle is positioned at 120xc2x0, the lens is set to ∞. And, as the zoom ring is further turned from the position of 120xc2x0, focusing is adjusted to the near distance in a range from the turning angle of 120xc2x0 through 150xc2x0, wherein the zoom lens is located at a position where the turning angle is 150xc2x0, and the lens focusing is set to the point-blank position.
Further, if the zoom ring is turned to a turning angle position of 180xc2x0, the power varying unit is set to the telephoto end. At this time, the lens is focused to ∞. As the zoom ring is further turned from the position where the turning angle is 180xc2x0, the positive lens unit 101 is moved in the optical axis direction based on the arrow C, and at the same time, the negative lens unit 103 is moved in the optical axis direction on the basis of the arrow M4, wherein focusing adjustment to the near distance of the lens group is carried out. Herein, when the zoom ring turning angle is positioned at 240xc2x0, the lens is focused to the near distance.
With the above-described construction, the magnification varying unit carries out varying the power and focusing adjustment by only turning a single zoom ring.
In a power varying unit that has been proposed in Japanese Patent No. Hei 6-100707 and a zoom position changing unit that has been proposed in Japanese Laid-Open No. Hei 9-80291, the amount of protrusion of lens groups (such as a positive lens unit 101 and a negative lens unit 103) is large when the lens focusing is varied from ∞ to the near distance at the telephoto end. Herein, if the amount of protrusion is large, the length of a cam groove to guide the lens groups in the optical axis direction becomes longer in the optical axis direction, wherein since the length of the cam barrel in the optical axis direction, in which the cam groove is formed, is increased in line therewith, the size of the lens barrel is increased. Also, if the amount of protrusion of the lens groups is large, it becomes inconvenient to handle the lens barrel.
It is therefore an object of the present invention to provide a lens barrel, the size of which is reduced, and at the same time, which can be easily handled, by decreasing the amount of protrusion of lens groups by varying the amount of movement of the lens group (which is located nearest to the object side) in the optical axis direction when carrying out focusing adjustment at the TELE end.
In order to achieve the above-described object, a variable power lens barrel according to one aspect of the invention includes a first lens unit that is positioned nearest to the object side, and a cam barrel having a first cam, wherein the first cam alternately and continuously has a plurality of variable power cam portions that drive the above-described first lens unit for varying power thereof in the optical axis direction and a plurality of focus cam portions that drive the above-described first lens unit driven by the respective variable power cam portions for focusing in the optical axis.
Herein, an amount of lift of the focus cam portion of the above-described first cam, which drives the above-described first lens unit, in the optical axis direction at the telephoto end is smaller than an amount of lift of the focus cam portion of the above-described first cam, which drives the above-described first lens unit, in the optical axis direction at other variable power positions.
The variable power lens barrel according to the above aspect of the invention further includes a second lens unit that is positioned at the image plane side nearer than the above-described first lens unit.
A second cam is formed in the above-described cam barrel.
The second cam alternately and continuously has a plurality of variable power cam portions that drive the above-described second lens unit for varying power thereof in the optical axis direction and a plurality of focus cam portions that drive the above-described second lens unit driven by the respective variable power cam portions for focusing in the optical axis direction.
Herein, an amount of lift of the focusing cam portion of the above-described second cam, which drives the above-described second lens unit, in the optical axis direction at the telephoto end is smaller than an amount of lift of the focus cam portion of the above-described second cam, which drives the above-described second lens unit, in the optical axis direction at other variable power positions.
Also, the variable power lens barrel according to the above aspect of the invention further includes a second lens unit that is positioned at the image plane side nearer than the above-described first lens unit.
A second cam is formed in the above-described cam barrel.
The second cam alternately and continuously has a plurality of variable power cam portions that drive the above-described second lens unit for varying power thereof in the optical axis direction and a plurality of focus cam portions that drive the above-described second lens unit driven by the respective variable power cam portions for focusing in the optical axis direction.
Herein, the focusing cam portion of the second cam that drives the above-described second lens unit at the telephoto end is located in a variable power lens barrel that drives the above-described second lens unit at a nearer image plane side than the position of the above-described second lens unit that has been driven to the telephoto end by the variable power cam portion of the above-described second cam.
Further, the above-described cam barrel is movable in the optical axis direction.
The lens barrel has a drive member having a third cam.
The third cam alternately and continuously has a plurality of variable power cam portions that drive the above-described cam barrel for varying the power in the optical axis direction, and a plurality of focusing cam portions that drive the above described cam barrel driven by the respective variable power cam portions for focusing in the optical axis direction.
Herein, the amount of lift of the focusing cam portion of the above-described third cam in the optical axis direction, which drives the above-described cam barrel at the telephoto end, is smaller than the amount of light of the focusing cam portion of the above-described third cam, which drives the above-described cam barrel at other power varying positions.
Still further features will be made apparent from the following drawings and description.